The jury is in on the future of NSW's Art Gallery, but the public won't know the winner until late May

An international jury including prestigious architects has unanimously chosen an architect to design a new wing of the Art Gallery of NSW, but the public won't be told whose design will change one of Sydney's most historic sites until late May.

The $450 million project called Sydney Modern – which would double the size of the gallery – would change the look of Sydney and create another huge highlight, said Michael Brand, the AGNSW's director and jury member.

In addition to creating a new wing, the shortlisted architects were asked to create a cultural precinct linked by landscaped gardens to include the Botanical Gardens, the State Library and the Domain, while maximising the site's views of the harbour.

For more than a week, the seven jurors, including Australian architect Glenn Murcutt, the American Toshiko Mori, Finland's Juhani Pallasmaa and landscape architect Kathryn Gustafson, have been locked in a room at the gallery overlooking the new site since they received the architects' concepts on Monday, April 6. Before reaching a unanimous decision on Thursday afternoon, they interviewed the architects, reviewed the designs and checked that the proposals, including the costings, met the brief.

The new precinct would connect the city to Woolloomooloo. The old gallery will also be connected to a new wing, that will very likely stretch from the landbridge over the Cahill Expressway to the old naval reservoir to the east of Mrs Macquaries Road. It is expected to include outdoor spaces suitable for live performances and displays of sculpture and other art.

The jurors had been looking for the missing piece of the puzzle. Each of the five finalists in the international architecture contest was required to bring a model of their proposal to fit in a metre by metre square maquette of the existing gallery on the site.

"This time they brought their models that slotted into a bigger site model," said Dr Brand displaying the wooden maquette. He said it had been a particularly useful way to visualise the new wing, and see the different ways that the five firms proposed joining the old to the new.

The five architects included three international firms, Kazuyo Sejima + Ryue Nishizawa / SANAA Tokyo, Kengo Kuma & Associates Tokyo and Paris, and RMA Architects Mumbai and Boston; and two Australian firms, Sean Godsell Architects Melbourne and Kerry Hill Architects from Singapore and Perth.

Dr Brand said the challenge was to build something that was architecturally of the highest international quality, while reflecting its location in Sydney.

"What was Sydney architecture?" he asked.

When [Jorn] Utzon designed the Opera House, there was nothing particularly Sydney about it, he said. Similarly the Harbour Bridge was chosen because it was a great piece of engineering.

The design should reflect the fact that it was in Sydney, and not in a tokenistic way where a visitor would see a few palm trees and the tip of the Harbour bridge in their snapshots.

The gallery's deputy director, Anne Flanagan, said the new wing would open to display the gallery's wide collection of Indigenous and Australian art, much of which is stored because of a lack of space or displayed with only a label of explanation.

"It is one thing putting a work on the wall with a label, but it is a whole other ballgame when you can see an Indigenous artist like Rusty Peters in his country talking about his work, it just comes to life."

The jury's recommendation won't be revealed to the public until after it is approved by the the NSW government and the firm has agreed and signed the contract.